#include "common.h"

class Solution
{
public:
    int mySqrt(int x)
    {
        if(x <= 1) return x;

        long long left = 0, right = x - 1;
        while(left < right)
        {
            long long  mid = left + (right - left + 1) / 2;
            if(mid * mid <= x) left = mid;
            else right = mid - 1;
        }
        return right;
    }
};